You may want to try obtaining the Windows 7 .iso file (by whatever means you have available), and create a boot-able USB drive to be able to boot into the copy of Windows 7 .iso file ( Solid program for creating a boot-able drive, https://rufus.akeo.ie/ ). After creating the boot-able drive, you'll want to make sure your laptop uses that USB drive as the boot drive, to do that you'll want to access the BIOs of your laptop. Upon booting of your laptop you should be prompted to hit a key to enter BIOs. Go ahead and do that, sadly BIOs are all very different depending on the manufacturer, so you'll want to find the place where you can select the drive your laptop will boot from, select the USB drive. Then Save>Exit. If your laptop doesnt automatically reboot, turn it on and it should boot from the USB drive prompting you to get a clean install of Windows 7. Now if you want my personal opinion, I would suggest upgrading to Windows 10, better performing Operating System and if you follow the link I provide, the upgrade won't delete any of your personal files. (Link as mentioned >> https://www.microsoft.com/en-us/software-download/windows10 )